Classical antennas range in length according to the operating wavelength. A fundamental dipole antenna is one-half wavelength long and monopoles (with an image antenna in the ground plane) are one-quarter wavelength long. High frequency (HF) communication in the 2-30 MHz range prefers a dipole antenna that ranges in length from 15 to 234 feet or a monopole that ranges in length from 8 to 117 feet. Shortening the physical and thus electrical length of an antenna (dipole or monopole) will exponentially lower the efficiency of the antenna, as well as drastically altering the impedance of the antenna, which can be matched to the radio's impedance to avoid significant loss of radio signals.
A monopole antenna is typically deployed as a vertical “whip” antenna, orthogonal to a surface (earth ground, ocean, metal surface, etc.). The monopole antenna is considered to be one-half of a classical dipole antenna, with the monopole itself comprising one-half of the dipole and the other half existing as a theoretical “image” monopole in the ground plane. Thus the monopole antenna's operation and performance is critically dependent upon the nature and conductive quality of the ground plane. In order to erect an efficient and useful antenna at HF frequencies, a large area free of obstructions is required.
However, HF radio communications are often required on vehicles, ships, aircraft and other movable platforms, most of which have a physical footprint that are significantly smaller than the physical length required by the classical dipole or monopole antennas to span the HF band of 2 to 30 MHz. Thus, an “electrically short” antenna is employed with the size tailored to fit the platform. When using such electrically short antennas a complex variable reactive impedance matching network (typically referred to as an “antenna coupler”) is required to transform the frequency-dependent impedance of the antenna to an approximation of the fixed impedance of the radio (typically 50 ohms) according to fulfillment of the optimum power transfer theorem. These devices are expensive, complexly require many moving adjustments to maintain matching impedance, and often require placement near the antenna where they are exposed to the environment.
What is required is an alternative antenna system that is simple to construct and maintain, and requires no complex antenna couplers.